The following materials are fully incorporated herein by reference: R. C. Hansen, Phased Array Antennas, Wiley-Interscience, New York, 1998; and R. J. Mailloux, Phased Array Antenna Handbook, Artech House, Boston, 2005.
The design of array antennas for monopulse radar tracking or search systems quite often requires optimization of the sum pattern-to-sidelobe level (SLL) ratio, while still maintaining high directivity of the sum beam. A difference beam may be provided as an auxiliary pattern with a boresight null coincident with the beam peak of the sum pattern. The tracking drive system adjusts the antenna position until the signal in the difference beam reaches a minimum, thereby causing the sum beam to point accurately at the radar target.
Most conventional monopulse radar systems implement a dish reflector/comparator combination to accomplish their antenna functions. Monopulse radar functionality is implemented with parabolic reflector antennas having waveguide comparators at their feed locations.
Some conventional monopulse systems use planar patch antenna arrays rather than relying solely on dish antennas. Low SLLs, on the order of 30 dB, have been realized with planar patch array technology over a 20% fractional bandwidth. These planar patch arrays are typically single port antennas with only a boresighted sum beam based on Taylor weights.
A Bayliss aperture distribution may be used to achieve low SLLs in the difference beam. Some efforts have been made to simplify methods for acquiring Bayliss and Taylor weights on the same antenna aperture. One approach proposes shaping the “aperture tails” of the Bayliss and Taylor distributions to be the same, in order to reduce the complexity of the feed network. However, in the context of a linear antenna array, this approach addresses less than half of the array's feeding. Other more complex systems, such as used by military ships and aircraft, employ active amplification in conjunction with phase shifters to obtain the desired magnitudes and phases. These military systems are typically implemented with coaxial cable or waveguide elements.
It is desirable in view of the foregoing to provide for an antenna array distribution network that provides distributions for sum or difference patterns across a radiating aperture in a monopulse radar system.